Fuel injector for low NOx and enhanced flame stabilization

ABSTRACT

A fuel injector for use in a furnace is provided. The fuel injector is used to deliver pulverized fuel to a combustion chamber of a furnace. The structure of the fuel injector facilitates efficient combustion while stabilizing the combustion flame. As a result, a minimal amount of NO x  and other undesirable byproducts are released into the atmosphere.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Patent Application60/551,143, filed Mar. 8, 2004, the disclosure of which is incorporatedby reference herein.

FIELD OF THE INVENTION

The present invention relates to fuel injectors for use in connectionwith a furnace. More particularly, the present invention relates to afuel injector and a furnace where pulverized coal or other solid fuel istransferred with a carrier gas and efficiently burned within acombustion chamber of the furnace so that the formation of NitrogenOxides (NO_(x)) and other undesirable by-products associated withunburned fuel are reduced.

BACKGROUND OF THE INVENTION

Low NO_(x) pulverized coal burners consist of a fuel injector andsecondary air register controls that have two or more passagewaysthrough which secondary air flows. The pulverized coal is carried by oneor more gasses, generally air, and passes through the fuel injector intothe furnace. The carrier gas is considered the primary air. However, theprimary air carrying the coal typically represents no more than 25% ofthe total combustion air required for combustion. The remainingcombustion air enters the furnace through secondary air registers. Inmany additional cases some of the secondary air is directed to separatestaging ports such as overfire air ports, to make combustion of the coalmore efficient.

Coal burners, particular low NO_(x) pulverized coal burners, mustdevelop a strong stable flame well rooted in the throat of the burners.Among the design problems typical of these types of burners aremaintaining their high reliability of the fuel injector while creating adistribution of pulverized coal and carrier (primary) air that minimizesthe generation of NO_(x), and creating a near zone aerodynamicstabilization pattern of the secondary combustion air that enters theburner around the fuel injector.

Many older designs use flame stabilizers, impellers or collecting portsin the coal stream to attempt create an optimal ratio of fuel/airdistributed into the burner. However, these arrangements are subject torapid wear of the parts, potential overheating and coking (undesiredbuild-up) of the coal on the parts and the resultant reduction inservice life. Further, as the parts wear their geometry changes andcauses the combustion to degrade.

In typical low NO_(x) burners the secondary air enters the burnerthrough two or more concentric passageways to create an “air staging”effect. Generally these designs include an inner and an outer secondaryair zone with adjustable swirl generators in each zone. Consequently,balancing and optimizing the air between the inner and outer zoneindependently of swirl is not attainable. These designs do not haveindependent means of optimizing the flow quantity and swirl in the innerversus outer secondary air zones.

Low NO_(x) burner designs separate the functions of fuel injection andsecondary air flow control into essentially independent functions, butintegrate the two assemblies into one burner. The fuel injector from onetype of burner is generally not transferable into a register assemblyfrom another burner design system.

SUMMARY OF THE INVENTION

The present invention solves problems associated with known low NO_(x)burner designs by providing a fuel injector with an uninterruptedpassageway through which pulverized fuel and its carrier gas flow.External flame stabilizers are arranged to provide excellent stabilityof the flame within the burner. A fixed vane swirler and an air controldamper are also arranged on the fuel injector to further control theflame produced upon combustion of the pulverized fuel. The present fuelinjector resolves the operational and reliability problems discussedabove. Further, such fuel injector can be utilized in virtually anyburner configuration: Circular burner arrangements as well as thevertically stacked linear burners typical of “corner” or “tangential”firing.

As used herein, the term “fuel injector” is intended to cover devicesused to transport pulverized fuel and a carrier gas to be burned withinan associated furnace. It should be appreciated that the term“pulverized fuel” is intended to cover various types of fuel suchpulverized coal or the like. While the term “pulverized coal” is usedfor convenience to describe a preferred embodiment, it is also intendedto encompass various types of pulverized fuels other than coal. Further,the term “carrier gas” covers gasses other than those present in air.However, since air is used to transport the pulverized coal inaccordance with a preferred embodiment of the present invention, theterm “primary air” will often be used herein and is intended toencompass various types of carrier gasses other than air.

The design of the fuel injector of the present invention has beendeveloped to enhance the performance and reliability of low NO_(x)burners. Thus, the design features of the present invention areapplicable to various types of low NO_(x) burner systems.

In accordance with a preferred embodiment of the present invention, afuel injector is provided for use in a furnace. The fuel injectorcomprises an inner barrel having inlet and outlet ends, and a passagewayextending between inlet and outlet ends through which a fuel streamincluding a carrier gas and fuel particles are permitted to flow. Theinner barrel is preferably free of obstructions between the inlet andoutlet ends such that the carrier gas and fuel particles can flowwithout interruption into an associated furnace. The fuel injectorpreferably comprises an outer barrel surrounding at least a portion ofthe inner barrel, and an outer passageway therebetween through whichsecondary air is permitted to flow. A plurality of stabilizer vanes arepreferably arranged within the outer passageway near the outlet end ofthe inner barrel. The secondary air flowing through the outer passagewaywill impact the stabilizer vanes and will help maintain combustion ofthe fuel streams near the outlet end of the inner barrel. A plurality ofaxial vanes are also preferably arranged within the outer passagewaybetween the inner and outer barrels. Each of the axial vanes arearranged between a corresponding pair of the stabilizer vanes, andfunction in concert with the stabilizer vanes to create desired flow ofthe secondary air with respect to the fuel stream flowing from theoutlet end. A fixed vane swirler is also preferably arranged within theouter passageway between the inner and outer barrels. The fixed vaneswirler includes a structure sufficient to impact the secondary air andcreate a rotational flow thereof around the stabilizer and axial vanes.

In another preferred embodiment, an air controlled damper may bearranged within the outer passageway form between the inner and outerbarrels. The air control damper may be structured and arranged tocontrol the quantity of the secondary air flowing through the fixed vaneswirler.

The stabilizer and axial vanes may be attached to the inner barrel, andthe fixed vane swirler may be attached to the outer barrel. However, thespecific arrangement of these features are optional and represent onepreferred embodiment.

The air control damper may comprise a perforated plate and an axiallymovable sleeve to permit selective control of the quantity of airpermitted to flow through the fixed vane swirler.

In another preferred embodiment, a furnace system is provided. Thefurnace may comprise a housing, a combustion zone arranged within thehousing, and one or more fuel injectors having the features discussedabove.

Low NO_(x) burner designs separate the functions of fuel injection andsecondary air flow control into essentially independent functions, butintegrate the two assemblies into one burner. The fuel injector from onetype of burner system cannot typically be integrated into a registerassembly of another burner design system design.

The present invention is a stand-alone fuel injector that includes itsown integral stabilization air flow controls and devices. Consequently,the present fuel injector can be inserted into various types of registerassemblies. The present fuel injector provides for improved flamestability, lower NOx output and better control of carbon monoxide andunburned carbon.

Accordingly, it is an object of the present invention to provide animproved fuel injector, and optionally an entire furnace, which providesa low NO_(x) output. It is another object to provide a fuel injector,and optionally a furnace system, having enhanced flame stabilization.These and other objects and advantages of the present invention will bemore readily understood when considered in conjunction with theaccompanying drawings and a detailed description of the preferredembodiments which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic combined cross-sectional and front view of theoutlet portion of a preferred embodiment of fuel injector of the presentinvention.

FIG. 2 is a cut-away perspective view of a preferred embodiment of thefuel injector of the present invention.

FIG. 3 is a cross-sectional schematic view of another embodiment of thefuel injector of the present invention illustrated in an installedposition with respect to a furnace.

FIG. 4 is a schematic cross-sectional view of another preferredembodiment of the fuel injector of the present invention shown in aninstalled position with respect to a furnace.

FIG. 5 is a front elevational view illustrating a corner-fired burnerarray showing a plurality of fuel injectors in accordance with thepresent invention.

FIG. 6 is a perspective front elevational view of a portion of anembodiment of the fuel injector of the present invention.

FIG. 7 is a perspective front elevational view of the embodiment of thefuel injector shown in FIG. 6 in a further assembled position within afurnace.

FIG. 8 is a schematic combined cross-sectional and front view of aplurality of fuel injectors in accordance with an embodiment of thepresent invention incorporated into a corner-fired array of a furnace.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1-8 of the drawings, the fuel injector 10 of thepresent invention is shown in various embodiments and views. In some ofthe views such as FIGS. 1 and 2, the fuel injector 10 is shown isolated.In other views such as FIGS. 5, 6, 7 and 8, the fuel injector 10 isshown incorporated into a furnace.

A preferred embodiment of the fuel injector 10 of the present inventionis illustrated in FIGS. 1 and 2. It includes an elongated inner barrel12 having an inlet end 16 and an outlet end 14. A segmented nozzledesign is arranged at the outlet end where a series of concave orelliptical shaped areas 18 function to generate multiple concentratedstreams of coal exiting the nozzle at the outlet end 14.

FIG. 2 illustrates that the fuel injector 10 includes an outer barrel20, which circumferentially surrounds the inner barrel 12 over at leasta portion thereof. Stabilizer vanes 22, axial vanes 24 and a fixed vaneswirler 26 are arranged in a passageway between the inner barrel 12 andouter barrel 20. The structure and operation of these components aredescribed further below.

An air control damper 28 is also arranged in the passageway between theinner barrel 12 and outer barrel 20. The air control damper assemblyincludes a perforated plate 30 and an axially movable sleeve 32. Acontrol arm 34 is connected to the movable sleeve for permitting anoperator to axially adjust it so that a desired amount of secondary aircan flow into and around the fixed vane swirler 26.

As also shown in FIGS. 2, 3 and 4, a connection flange 36 is arranged atthe inlet end 16 of the fuel injector 10. The connection flange 36 maybe used to connect the fuel injector 10 to an elbow or other conduit forproviding a carrier gas and pulverized fuel particles to the innerbarrel 12.

FIGS. 5, 7 and 8 illustrate the fuel injector 10 (or a plurality of fuelinjectors 10) as part of an overall furnace assembly 38. When arrangedwithin such a furnace, the fuel injector 10 may include an air blockingplate 40 (as shown in FIGS. 6 and 7) to assure optimal performance.

Low NO_(x) flame stabilization nozzle 15 is an important element forobtaining excellent flame stability and minimum NOx output. FIG. 1 showsthe segmented coal nozzle, which has an open design with no obstructionsto collect coal. Pressure drop is low, and there are no components inthe coal path that are subject to wear, coal accumulation or coking.Excellent flame stability is achieved due to the external flamestabilizers surrounding each segment.

Stabilizer and axial vanes 22 and 24 act in combination to create acomplex flow of secondary air from the inner zone over and around thefuel streams leaving the nozzle 15. The effect is to create an initialstabilization zone close to the fuel injector nozzle 15.

FIG. 2 illustrates the complete fuel injector assembly 10 with thelocations of the flame stabilizers including the combination ofcircumferential curved stabilizer vanes 22 and axial vanes 24), a fixedvane swirler 26 and an air control damper 28. The functions of thesedevices are described below.

Flame stabilizers function as previously described in U.S. Pat. No.5,762,007, the disclosure of which is incorporated herein by reference.In general, FIGS. 1-8 illustrate the curved stabilizer vanes 22 andlongitudinal axial vanes 24, which are arranged within the outerpassageway (between the inner and outer barrels 12 and 20, near theoutlet end 14 of the inner barrel 12. As clearly shown in FIGS. 1 and 2,a gap may be maintained between adjacent curved stabilizer vanes 22 toallow secondary air to pass through. The combination of the curvedstabilizer vanes 22 and the axial vanes 24 function as flamestabilizers, which help assure that the flame created upon combustion ofthe fuel streams exiting the nozzle 15 is “well-rooted” close to theoutlet end of the fuel injector 10. Thus, maximum flame stability andundesirable by-products such as NO_(x) and CO are minimized. Thesecondary air flowing between the inner and outer barrels 12 and 20impact the curved stabilizer vanes 22 and are guided by the axial vanes24. This creates eddy flows, which minimize interference with theprimary pulverized coal stream while still facilitating enhancement ofthe resulting flame.

The fixed vane swirler 26 is attached to the outer barrel 20 of the fuelinjector 10. The position of the swirler 26 is constant and noadjustments are required. It provides rotation to the air that flowsover the flame stabilizers 22 and enhances their effect in controllingthe root of the flame formed by the coal leaving the nozzle 15.

Air control damper 28 includes perforated plate 30 surrounded by anaxially movable sleeve 32. The damper is operable to control thequantity of air flowing through the fixed vane swirler 26 and over theflame stabilizers 22 surrounding the nozzle 15. The axially movablesleeve 32 is connected to a control arm 34, which permits control of thequantity of air flow and allows for the optimization of the flameposition and internal stoichiometry in the region close to the burner ofthe furnace 38.

The fuel injector assembly 10 with its own air flow controls representsan independent assembly that is no longer required to be installed as anintegral part of one specific burner geometry. Thus it can be used inconjunction with a relatively simple single register assembly which,when combined with the presently disclosed fuel injector assembly,completes the two stage secondary air aerodynamics typical of low NO_(x)burners.

The fixed vane swirler 26 is attached to the outer barrel 20 of the fuelinjector 10. The position of the swirler is fixed and no adjustments arerequired.

FIG. 3 illustrate an embodiment of a dual register that uses an radialshaft main register within a furnace system. In this assembly a singleregister including radial shaft spin vanes to control outer zonesecondary air swirl and a sleeve damper to control the total quantity ofsecondary air entering the burner, is combined with the fuel injector 10and its secondary air controls to form a complete low NO_(x) burner.

FIG. 4 illustrates another embodiment where the present enhanced flamestabilization fuel injector 10 is integrated into a register assemblythat utilizes an axial shaft main register. The enhanced flamestabilization fuel injector 10 is inserted into the respective mainregister assembly with minimal modification. Due to the consistent nearzone aerodynamic conditions afforded by the designs disclosed herein,the performance of each of these burner configurations is substantiallythe same even though the overall geometry is different.

An alternate type of combustion system is shown in FIG. 5—a corner-firedburner system. In this system the burners consist of a vertical array ofalternating secondary air injection nozzles, usually of a square orrectangular geometry, and fuel injectors 10. In a conventionalarrangement the fuel injectors are also of square or rectangularconfiguration. However the present enhanced flame stabilization fuelinjector 10 can be installed in substitution for the standard design toprovide the same reliability and combustion conditions that result fromuse of this technology in the circular burners.

In the corner-fired arrangement a secondary air flow divider isintegrally installed around the present enhanced flame stabilizationfuel injector 10 to direct the secondary air over the integral fixed vanswirler 26. An air blocking plate is attached to the flow divider toprevent secondary air from bypassing around the outside of the flowdivider and, thereby, not passing through the fixed vane swirler 26 thatis inside the flow divider and between it and the coal nozzle 15.

FIG. 8 illustrates the complete corner burner array with the presentenhance flame stabilization fuel injector 10 assemblies shown integralto the array.

The present enhanced flame stabilization fuel injector 10 discloses afuel injector assembly that can be incorporated into a wide variety ofpulverized coal burner types while maintaining the conditions foroptimal aerodynamics and fuel flow to assure minimal NO_(x) generationwithout compromising combustion performance.

It should be appreciated that various modifications to the configurationand size of the present fuel injector 10 and associated furnace systemmay be made to the preferred embodiment of the present invention withoutdeparting from the scope thereof as defined in the claims set forthbelow.

1. A fuel injector for use in a furnace, said fuel injector comprising:(a) an inner barrel having inlet and outlet ends, said inner barreldefining a passageway extending between said inlet and outlet endsthrough which a fuel stream including carrier gas and fuel particles arepermitted to flow; (b) an outer barrel surrounding at least a portion ofsaid inner barrel and defining an outer passageway through whichsecondary air is permitted to flow; (c) a plurality of stabilizer vanesarranged within said outer passageway near said outlet end of said innerbarrel, the secondary air flowing through the outer passageway impactssaid plurality of stabilizer vanes such that combustion of the fuelstream is maintained near said outlet end of said inner barrel; (d) aplurality of axial vanes arranged within said outer passageway betweensaid inner and outer barrels, each of said axial vanes being arrangedbetween a corresponding pair of said stabilizer vanes, and functioningin concert with said stabilizer vanes to create a desired flow of thesecondary air with respect to the fuel stream flowing from said outletend; and (e) a fixed vane swirler arranged within said outer passagewaybetween said inner and outer barrels, said fixed vane swirler having astructure sufficient to create a rotational flow of the secondary airaround said plurality of stabilizer and axial vanes.
 2. The fuelinjector of claim 1 further comprising an air control damper arrangedwithin said outer passageway structured and arranged to control thequantity of the secondary air flowing through said fixed vane swirler.3. The fuel injector of claim 1 wherein said plurality of stabilizervanes are attached to said inner barrel.
 4. The fuel injector of claim 1wherein said plurality of axial vanes are attached to said inner barrel.5. The fuel injector of claim 1 wherein said fixed vane swirler isattached to said outer barrel.
 6. The fuel injector of claim 2 whereinsaid air control damper comprises a perforated plate and an axiallymovable sleeve.
 7. The fuel injector of claim 1 wherein said outlet endof said inner barrel includes a plurality of elliptical sections adaptedto create a plurality of concentrated fuel streams at said outlet end ofsaid inner barrel.
 8. A furnace comprising: (a) a housing; (b) acombustion zone within said housing; and (c) a fuel injector arranged todeliver at least one fuel stream to said combustion zone, said fuelinjector including: (1) an inner barrel having inlet and outlet ends,said inner barrel defining a passageway extending between said inlet andoutlet ends through which a fuel stream including carrier gas and fuelparticles are permitted to flow, (2) an outer barrel surrounding atleast a portion of said inner barrel and defining an outer passagewaythrough which secondary air is permitted to flow, (3) a plurality ofstabilizer vanes arranged within said outer passageway near said outletend of said inner barrel, the secondary air flowing through the outerpassageway impacts said plurality of stabilizer vanes such thatcombustion of the fuel stream is maintained near said outlet end of saidinner barrel, (4) a plurality of axial vanes arranged within said outerpassageway between said inner and outer barrels, each of said axialvanes being arranged between a corresponding pair of said stabilizervanes, and functioning in concert with said stabilizer vanes to create adesired flow of the secondary air with respect to the fuel streamflowing from said outlet end, and (5) a fixed vane swirler arrangedwithin said outer passageway between said inner and outer barrels, saidfixed vane swirler having a structure sufficient to create a rotationalflow of the secondary air around said plurality of stabilizer and axialvanes.
 9. The fuel injector of claim 8 further comprising an air controldamper arranged within said outer passageway structured and arranged tocontrol the quantity of the secondary air flowing through said fixedvane swirler.
 10. The fuel injector of claim 8 wherein said plurality ofstabilizer vanes are attached to said inner barrel.
 11. The fuelinjector of claim 8 wherein said plurality of axial vanes are attachedto said inner barrel.
 12. The fuel injector of claim 8 wherein saidfixed vane swirler is attached to said outer barrel.
 13. The fuelinjector of claim 9 wherein said air control damper comprises aperforated plate and an axially movable sleeve.
 14. The fuel injector ofclaim 8 wherein said outlet end of said inner barrel includes aplurality of elliptical sections adapted to create a plurality ofconcentrated fuel streams at said outlet end of said inner barrel. 15.The furnace of claim 1 further comprising a plurality of fuel injectors.16. The fuel injector of claim 15 further comprising an air controldamper arranged within said outer passageway structured and arranged tocontrol the quantity of the secondary air flowing through said fixedvane swirler.